1. Field of the Invention
The present invention relates to a method and apparatus for continuously generating and forming carbon fiber (fibrous carbon) such as carbon nanotubes, graphite nanotubes, or the like.
2. Description of the Related Art
A carbon nanotube, which is a type of carbon fiber, is a material in the shape of a tube having a configuration wherein graphite structures are wound in the shape of a cylinder, and is a new material which is expected to be applied to various fields due to unique properties thereof. FIG. 2 illustrates a conventional method for generating carbon nanotubes employing the arc method disclosed in Japanese Patent Laid-Open No. 6-280116. As shown in FIG. 2, DC arc discharge in an inert gas with a carbon material, such as graphite or the like, being used as an anode 2, and a heat-resisting electroconductive material being used as a cathode 3, causes evaporation of the carbon material on the side of the anode 2 that reaches high temperature. Generally half of the evaporated carbon condenses in the gas phase, and soot, carbon nanotubes, and the like, are formed on the inner wall of the container. The other half of the evaporated carbon directly condenses at the tip of the cathode 3, and a hard carbonaceous deposited substance 16 is formed. Conventionally, the deposited substance 16 formed on the inner wall of the container and the tip of the cathode 3 is collected to manufacture carbon nanotubes. In FIG. 2, reference numeral 4 denotes an inert gas introducing port for introducing an inert gas into the container, and reference numeral 8 denotes a current supplying device for applying a voltage between the anode 2 and the cathode 3 so as to cause arc discharge.
The carbon nanotubes obtained with the above-described conventional arc discharge method are deposited on the inner wall of the container (the cathode 3). Accordingly, a collecting method is required, thus leading to an increase of process steps. Furthermore, with the conventional arc discharge method, since deposition of the carbon material occurs on the cathode 3, there is a need to perform arc discharge while adjusting the distance between the anode 2 and the cathode 3 corresponding to the deposition amount of the cathode deposited substance 16. Accordingly, the distance between the anode 2 and the cathode 3 cannot be fixed to be constant due to the growth of the cathode deposited substance 16, resulting in unstable discharge. Furthermore, the yield of the carbon nanotubes is low due to the generated cathode deposited substance 16 being exposed to arc discharge for a long time. Furthermore, while carbon nanotubes are contained in the deposited substance 16 generated by the arc discharge or the like, the generated carbon nanotubes tends to be aggregated (coagulated). Accordingly, in the event that carbon nanotubes are to be formed into a film on a substrate, there is a need to perform dispersion processing.
Furthermore, among methods for forming a film of carbon fibers such as carbon nanotubes on a substrate, a method is disclosed in Japanese Patent Laid-Open No. 2000-086216, whereby a catalytic metal film is formed, and is patterned so that the catalysis occurs at desired positions, and carbon nanotubes are formed by performing thermal processing by the CVD method, with the catalytic metal as a nucleus. Additionally another method is disclosed in Japanese Patent Laid-Open No. 2000-057934, whereby an auxiliary agent is applied to the substrate, and carbon nanotubes are formed at desired positions on the substrate by performing thermal processing with the electric field application plasma CVD method. However, with any of these methods, the number of process steps is great, leading to high costs.
With the conventional manufacturing methods, in a case of manufacturing carbon fibers such as carbon nanotubes or the like by the arc discharge method, for example, the carbon fiber is deposited on the inner wall, cathode, and the like, in the arc discharge container, and the deposited substance is collected for manufacturing a carbon material containing carbon fiber. As a result, the carbon fibers cannot be continuously manufactured, leading to an increase of process steps. Furthermore, the deposited substance containing carbon fibers formed on the inner wall of the container or the cathode tends to be aggregated (coagulated). Consequently, there was a need to perform dispersion processing.
Examples of the methods for forming a film of carbon fibers on a substrate include a method whereby dot-shaped patterning of a catalytic metal is performed at desired positions using resist so as to form a catalyst at desired positions for forming carbon fibers such as carbon nanotubes by performing thermal processing by the CVD method, with the catalytic metal as a nucleus, and a method wherein an auxiliary agent (catalysis) is applied to the substrate, and carbon fibers such as carbon nanotubes are formed at desired positions on the substrate with the electric field application plasma CVD method. However, any of these methods has a great number of process steps, leading to high costs.